This invention relates to planographic printing, especially lithographic printing. Particularly, although not exclusively, it relates to the correction of mistakes or other imperfections on printing members, for example printing plates, by rendering ink accepting areas non-ink accepting.
Our co-pending applications PCT/GB96/02883 (U.S. Pat. No. 6,105,500), PCT/GB98/01500, and PCT/GB98/01496, all three of which are incorporated herein by reference, describe a printing plate that comprises a support provided with a hydrophilic layer comprising a binder based on a material having Sixe2x80x94O bonds in which particulate material is dispersed and an image layer over the hydrophilic layer. Such a hydrophilic layer can advantageously be applied to a wide range of different support materials, for example metals such as aluminum; plastics, such as polyester; and also paper. Printing plates including a hydrophilic layer as described have excellent printing properties. However, a problem has now been noted in relation to the rendering of ink accepting areas non-ink accepting as may be required to correct mistakes or other imperfections on the printing plates.
It is well-known in the printing industry to remove or delete unwanted image material utilizing a deletion fluid, which may be applied to areas to be removed using a brush, a pen or other means. Known deletion fluids for negative plates commonly utilize a hydrogen fluoride solution in combination with an organic solvent and other additives. Hydrogen fluoride based deletion fluids generally remove image material very well. However, it has been noted that, in relation to plastic plates comprising a hydrophilic layer of the type described above, although most or all of an unwanted image area to which a known deletion fluid is applied is rendered non-ink accepting, there is often an area associated with and/or close to the unwanted image area which should be non-ink accepting but is found to be ink accepting. Consequently, such an area accepts ink during printing and leads to imperfections in printed material.
The inadequacies of hydrogen fluoride based deletion fluids in relation to hydrophilic layers of the type described have, to the applicant""s knowledge, been unappreciated in the past and, furthermore, the reasons for the apparent inadequate deletion of unwanted image areas using hydrogen fluoride based deletion fluids have not been investigated.
This invention is based on an appreciation of the existence of a problem with commercially-available hydrogen fluoride based deletion fluids and, additionally, on the discovery of the reasons for the problem. More particularly, it has been discovered that commercially-available hydrogen fluoride deletion fluids attack the aforesaid hydrophilic layer at a greater rate than that at which they attack the image layer and, consequently, the hydrophilic layer is removed in localized regions contacted by the deletion fluid. Such localized regions may be cosmetically undesirable because they imply a defective hydrophilic layer, and they may be undesirable from a performance perspective because they may be less hydrophilic and/or have a different ink-water balance compared to other regions of the plate and/or they may be more prone to wear.
The invention is a method of rendering non-ink accepting a selected ink accepting area of a printing member comprising a support and a hydrophilic layer that comprises a material having Sixe2x80x94O bonds and an image layer. The method comprises contacting the area with a means (hereinafter xe2x80x9cthe hydrophilizing meansxe2x80x9d) that renders the area non-ink accepting at a greater rate than that at which it can remove the hydrophilic layer.
The hydrophilic layer may be removed by the hydrophilizing means at a rate of less than 0.15 xcexcm.sxe2x88x921, typically less than 0.1 xcexcm.sxe2x88x921, preferably less than 0.05 xcexcm.s1xe2x88x921, more preferably less than 0.02 um.sxe2x88x921.
The ink-accepting area may be rendered non-ink accepting within 3 minutes, typically 2 minutes, preferably 1xc2xd minutes, more preferably within 1 minute, especially within 30 seconds or less of the first contact with the hydrophilizing means.
The rate of rendering of the ink-accepting area non-ink accepting may be at least 5 times, preferably at least 10 times, more preferably at least 20 times, especially at least 30 times the rate of removal of the hydrophilic layer. The relative rates of these processes can be readily compared by visual inspection. A printing member comprising a support, a hydrophilic layer, and a non-ink accepting area is treated with a hydrophilizing means and relative rates visually determined.
In a first embodiment, contact with the hydrophilizing means renders the ink accepting area non-ink accepting by removing the area.
The ink-accepting area may be removed at a rate of greater than 0.005 gmxe2x88x922sxe2x88x921, preferably greater than 0.01 gmxe2x88x922sxe2x88x921, more preferably greater than 0.05 gmxe2x88x922sxe2x88x921.
The thickness of the ink-accepting area may be at least 0.4 xcexcm, preferably at least 0.8 xcexcm, more preferably at least about 1 xcexcm. The thickness of the ink-accepting area may be less than 10 xcexcm, typically less than 8 xcexcm, preferably less than 6 xcexcm, more preferably less than 4 xcexcm, especially less than 2 xcexcm or less.
Preferably, in the method, substantially the whole thickness of the ink-accepting area is removed, thereby to reveal an underlying layer which is non-ink accepting and which is typically the hydrophilic layer.
The hydrophilizing means may include one or more of acids and/or alkalis and/or oxidizing formulations.
Preferred acids include strong acids, for example inorganic acids such as sulfuric or nitric; weak inorganic acids, for example phospho-acids such as orthophosphoric; and organic acids for example carboxylic acids such as acetic and acrylic. Solutions comprising greater than 60%, preferably 70%, more preferably 80%, especially 90% of a the acid may be used. An especially preferred acid is sulfuric acid.
Preferred alkalis include sodium hydroxide, potassium hydroxide and silicates such as sodium silicate.
Preferred oxidizing formulations may include nitrites such as sodium nitrite; nitrates such as aluminum or potassium nitrate; halogen-based oxidizers for example peracids such as perchloric acid, perhalates such as periodates and perchlorates; hydrogen peroxide; transition metal oxidizing agents such as potassium permanganate, ferric chloride and chromium VI oxide.
The hydrophilizing means may include means for softening the hydrophilic layer.
The hydrophilizing means may include one or more solvents. Suitable solvents may include one or more of water; acids, typically of the type described above; and organic solvents, especially alcohols such as C1-3 alcohols and/or alkoxyalcohols such as 2-butoxyethanol, cyclohexanone, N-methylpyrrolidone, gamma-butyrolactone, dimethyl sulfoxide and benzylalcohol.
The hydrophilizing means may include a thickener.
Components of the hydrophilizing means may be applied together or may be applied one after the other.
Especially preferred hydrophilizing means may include one or more of sulfuric acid, hydrogen peroxide, nitrates, transition metal oxidizing agents, potassium hydroxide and a silicate especially sodium silicate.
In a second embodiment, contact with the hydrophilizing means renders the ink-accepting area non-ink accepting by covering the area. In this case, the hydrophilizing means may comprise any material or materials which can be bonded to the image layer and which is/are non-ink accepting. The hydrophilizing means may comprise a first material, which is applied directly to the ink-accepting area, and a second material, which is arranged over the first material. For example, the first material may be provided to aid adhesion of the second material to the ink-accepting area.
The hydrophilizing means of the second embodiment may include one or more materials selected from a silicate material; a silicone based material; a hydrophilic polymeric material, especially an organic material such as gelatin, polyvinyl alcohol (PVA) or polyvinyl pyrrolidone (PVP); or a sol or a gel material. The aforesaid hydrophilizing means are collectively referred to hereinafter as xe2x80x9cbinder meansxe2x80x9d.
The hydrophilizing means preferably comprises a fluid that is transformed to a non-fluid state after contact with the area. For example, the fluid may be transformed into a film after contact.
The hydrophilizing means may include a plurality of layers of material.
The hydrophilic layer of the printing plate which includes Sixe2x80x94O bonds may have an average thickness of less than 100 xcexcm, typically less than 50 xcexcm, preferably less than 20 xcexcm, more preferably less than 10 xcexcm, especially less than 5 xcexcm. In some cases the hydrophilic layer may have an average thickness of less than 3 xcexcm. The hydrophilic layer may have an average thickness of greater than 0.1 xcexcm, typically greater than 0.3 xcexcm, preferably greater than 0.5 xcexcm, more preferably greater than 1 pxcexcm.
The Ra of the hydrophilic layer may be measured using a Talysurf Plus fitted with a 112/2564-430 head, supplied by Rank Taylor Hobson Inc., Leicester, U.K. The Ra may be at least 0.2 xcexcm, typically at least 0.25 xcexcm, preferably at least 0.3 xcexcm, more preferably at least 0.35 xcexcm, especially at least 0.4 xcexcm. The Ra may be less than 1.5 xcexcm, typically less than 1 xcexcm, preferably less than 0.8 xcexcm, more preferably less than 0.7 xcexcm, especially less than 0.6 xcexcm, most preferably less than 0.5 xcexcm.
The hydrophilic layer may include 1 to 20 g of material per meter squared of substrate. Preferably the layer includes 3 to 20 g, more preferably 5 to 18 g, of material per meter squared of substrate. Most preferably, the layer includes 8 to 16 g of material/meter2.
The hydrophilic layer may include a binder material. The binder material preferably includes the material having Sixe2x80x94O bonds. The binder material may be a component of a polymeric material that includes Sixe2x80x94O bonds. The polymeric material may include xe2x80x94Sixe2x80x94Oxe2x80x94Sixe2x80x94, especially xe2x80x94Sixe2x80x94Oxe2x80x94moieties.
At least 50 wt %, typically at least 60 wt %, preferably at least 70 wt %, more preferably at least 80 wt %, especially at least 90 wt % of the binder material is made up of a polymeric material having Sixe2x80x94O bonds as described. Preferably, the binder material consists essentially of a polymeric material having Sixe2x80x94O bonds as described.
The binder material may make up at least 5 wt %, preferably at least 10 wt %, more preferably at least 15 wt %, especially at least 20 wt % of the hydrophilic layer. The binder material may make up less than 50 wt %, preferably less than 40 wt %, more preferably less than 30 wt %, especially less than 25 wt %, of the hydrophilic layer.
The binder material may be derived or derivable from a silicate material for example water glasses, metasilicates, orthosilicates, sesquisilicates and modified silicates such as borosilicate and phosphosilicate. The binder material is preferably derived or derivable from a silicate solution.
The binder material preferably includes less than 10 wt %, preferably less than 5 wt %, more preferably less than 1 wt %, especially substantially no, organic material, for example polymeric organic material.
Preferably, particulate material is provided in the hydrophilic layer, for example by being dispersed in the binder material thereof. Typically 30 to 85 wt %, preferably 40 to 80 wt %, more preferably 50 to 80 wt %, especially 60 to 80 wt %, of the hydrophilic layer is composed of the particulate material.
The particulate material may be organic or inorganic. Organic particulate materials may be provided by latexes. Inorganic particulate materials may be selected from alumina, silica, silicon carbide, zinc sulfide, zirconia, barium sulfate, talcs, clays (e.g. kaolin), lithopone and titanium oxide.
The particulate material may comprise a first particulate material. The first material may have a hardness of greater than 8 Modified Mohs (on a scale of 0 to 15), preferably greater than 9 and, more preferably, greater than 10 Modified Mohs. The first material may comprise generally spherical particles. Alternatively, the material may comprise flattened particles or platelets. The first material may have a mean particle size of at least 0.1 xcexcm, preferably at least 0.5 xcexcm and, more preferably, at least 1.0 xcexcm. The first material may have a mean particle size of less than 200 xcexcm, typically less than 100 xcexcm, preferably less than 45 xcexcm, more preferably less than 20 xcexcm, especially less than 10 xcexcm, and, most preferably, less than 5 xcexcm. The particle size distribution for 95% of particles of the first material may be in the range 0.01 to 150 xcexcm, preferably in the range 0.05 to 75 xcexcm, more preferably in the range 0.05 to 30 xcexcm. The first material preferably comprises an inorganic material. The first material preferably comprises alumina which term includes Al2O3 and hydrates thereof, for example Al2O3. 3H2O. Preferably, the material is Al2O3.
The hydrophilic layer may include at least 10 wt %, typically at least 20 wt %, preferably at least 25 wt %, more preferably at least 30 wt %, especially at least 35 wt % of the first particulate material. The hydrophilic layer may include less than 80 wt %, typically less than 70 wt %, preferably less than 60 wt %, more preferably less than 50 wt %, especially less than 40 wt % of the first particulate material.
The ratio of the wt % of the first particulate material to binder material may be in the range 0.5 to 2, preferably in the range 1 to 2, more preferably in the range 1.4 to 1.8.
The particulate material may comprise a second particulate material. The second material may have a mean particle size of at least 0.001 xcexcm, typically at least 0.005 xcexcm, preferably at least 0.01 xcexcm, more preferably at least 0.05 xcexcm, especially at least 0.1 xcexcm. The second material may have a mean particle size of less than 200 xcexcm, typically less than 100 xcexcm, preferably less than 50 xcexcm, more preferably less than 10 xcexcm, especially less than 1 xcexcm, most preferably less than 0.5 xcexcm. The second material is preferably a pigment. The second material is preferably inorganic. The second material is preferably titanium dioxide.
The first and second particulate materials preferably define a multimodal, for example a bimodal particle size distribution.
The ratio of the wt % of the first particulate material to the second particulate material may be in the range 0.3 to 3, preferably 0.5 to 2, more preferably 0.75 to 1.33, especially about 1 to 1.
The hydrophilic layer may include at least 10 wt %, typically at least 20 wt %, preferably at least 25 wt %, more preferably at least 30 wt %, especially at least 35 wt % of the second particulate material. The hydrophilic layer may include less than 80 wt %, typically less than 70 wt %, preferably less than 60 wt %, more preferably less than 50 wt %, especially less than 40 wt % of the second particulate material. The ratio of the wt % of the second particulate material to binder material may be in the range 0.5 to 2, preferably in the range 1 to 2, more preferably in the range 1.4 to 1.8.
The hydrophilic layer may include one or more additional materials for improving its adhesion to a support, especially a plastic support. A preferred additional material is organic and is preferably polymeric. Resins are preferred.
The hydrophilizing means of the second embodiment described above may include additives to adjust its properties. For example, it may include materials for aiding deposition and/or abrasion resistance and/or for aiding the masking of the selected ink-accepting area and/or for aiding the hardening or curing or drying of the binder means. The hydrophilizing means may include first and/or second particulate materials, which may be as described in any statement herein.
Preferably, the binder material of the hydrophilic layer and the binder means of the hydrophilizing means include some or all of the same components. In a preferred embodiment, the binder material of the hydrophilic layer is derived from a silicate material and the binder means of the hydrophilizing means is also derived from the same silicate material. At least 50 wt %, typically at least 60 wt %, preferably at least 70 wt %, more preferably at least 80 wt %, especially at least 90 wt % of the composition of the hydrophilic layer is the same as that of the hydrophilizing means.
The support may comprise a metal layer. Preferred metals include aluminum, zinc and titanium, with aluminum being especially preferred. The support may comprise an alloy of the aforesaid metals. Other alloys that may be used include brass and steel, for example stainless steel.
The support may comprise a non-metal layer. Preferred non-metal layers include layers of plastic, paper or the like. Preferred plastics include polyester, especially polyethylene terephthlate.
The support may include one or a plurality of layers. Where the support comprises a plurality of layers, it may comprise a plastic, paper or textile layer and another layer. The other layer may be a metal layer, typically of a type described above. In this case, the support may comprise a metal to plastic or paper laminate; or metal may be applied by other means to plastic or paper, for example by sputtering or the like.
The image layer may comprise any known photosensitive material whether arranged to form a positive or negative plate. Examples of photosensitive materials include diazonium materials, polymers that undergo depolymerization or addition photopolymerization and silver halide gelatin assemblies. Examples of suitable materials are disclosed in: GB 1,592,281; GB 2,031,442 [Vikesland, U.S. Pat. No. 4,247,616]; GB 2,069,164; GB 2,080,964; GB 2,109,573; EP 0,377,589; Shiba, U.S. Pat. No. 4,268,609; and Watkiss, U.S. Pat. No. 4,567,131. The image layer is preferably arranged to form a negative plate.
In second aspect, the invention is a method of preparing a printing member for printing, the method comprising rendering non-ink accepting selected ink accepting areas of the member. The method preferably includes the step of causing printable information to become associated with a substrate, for example by information-wise exposing a non-exposed printing member, and inspecting the member to determine the selected ink-accepting areas to be rendered non-ink accepting.
The printing member preferably includes a hydrophilic layer prepared by contacting a support with a fluid comprising a silicate liquid in which particulate material is dispersed.
The silicate liquid may comprise a solution of any soluble silicate including compounds often referred to as water glasses, metasilicates, orthosilicates and sesquisilicates. The silicate liquid may comprise a solution of a modified silicate for example a borosilicate or phosphosilicate.
The silicate liquid may comprise one or, more preferably only one, metal or non-metal silicate. A metal silicate may be an alkali metal silicate. A non-metal silicate may be quaternary ammonium silicate.
The silicate liquid may be formed from silicate in which the ratio of the number of moles of silicon-containing species, for example SiO2, to the number of moles of cationic, for example metal, species is in the range 0.25 to 10, preferably in the range 0.25 to about 6, more preferably in the range 0.5 to 4.
The silicate liquid is preferably alkali metal silicate. In this case, the ratio of the number of moles of SiO2 to the number of moles of M2O in the silicate, where M represents an alkali metal may be at least 0.25, typically at least 0.5, preferably at least 1, more preferably at least 1.5. Especially preferred is the case in which the ratio is at least 2.5. The ratio may be less than 6, preferably less than 5 and more preferably less than 4.
Preferred alkali metal silicates include lithium, sodium and potassium silicates, with lithium and/or sodium silicate being especially preferred. A silicate liquid comprising only sodium silicate is most preferred.
The fluid may comprise 2 to 30 wt % of silicate (e.g. dissolved sodium silicate solid), preferably 5 to 20 wt %, more preferably 8 to 16 wt %. The liquid may be prepared using 10 to 60 wt %, preferably 30 to 50 wt %, more preferably 35 to 45 wt % of a silicate solution which comprises 30 to 40 wt % silicate.
The fluid may include 5 to 60 wt % of particulate material. Preferably, the fluid includes 10 to 50 wt %, more preferably 15 to 45 wt %, especially 20 to 40 wt % of particulate material.
The ratio of the weight of silicate to the weight of particulate material in the fluid is preferably in the range 0.1 to 2 and, more preferably, in the range 0.1 to 1. Especially preferred is the case in which the ratio is in the range 0.2 to 0.6.
The fluid may include more than 20 wt %, preferably more than 30 wt %, more preferably more than 40 wt %, especially more than 45 wt % water (including water included in the silicate liquid). The fluid may include less than 80 wt %, preferably less than 70 wt %, more preferably less than 65 wt %, especially less than about 60 wt % water.
Where the fluid comprises a silicate and the particulate material comprises the first material and the second material, the ratio of the wt % of silicate (e.g. dissolved sodium silicate solid) to the wt % of the first material may be in the range 0.25 to 4, preferably in the range 0.5 to 1.5 and more preferably about 1. Similarly, the ratio of the wt % of silicate to the wt % of the second material may be in the range 0.25 to 4, preferably in the range 0.5 to 1.5 and more preferably about 1. The ratio of the wt % of first material to the wt % of second material may be in the range 0.5 to 2, preferably in the range 0.75 to 1.5, more preferably about 1 to 1.
The particulate material may include a third material which is preferably adapted to lower the pH of the fluid. The third material may be a colloid, typically colloidal silica or an inorganic salt, typically a phosphate, with aluminum phosphate being preferred. Preferably less than 30wt %, more preferably less than 20wt %, especially less than 10 wt % of the total particulate material in the fluid is comprised by the third material.
The pH of the fluid may be greater than 9.0, is preferably greater than 9.5 and, more preferably, greater than 10.0. Especially preferred is the case in which the pH is greater than 10.5. The pH is typically controlled so that the silicate remains in solution and does not form a gel. A gel is generally formed when the pH of a silicate solution falls below pH 9. The pH of the fluid is preferably less than 14, more preferably less than 13.
The fluid may include other compounds for adjusting its properties. For example, the fluid may include one or more surfactants. The fluid may include 0 to 1 wt % of surfactant(s). A suitable class of surfactants comprises anionic sulfates or sulfonates. The fluid may include viscosity builders for adjusting the viscosity of the liquid. The fluid may include 0 to 10 wt %, preferably 0 to 5 wt % of viscosity builder(s). Also, the fluid may include dispersants for dispersing the inorganic particulate material throughout the fluid. The fluid may include 0 to 2 wt % of dispersant(s). A suitable dispersant may be sodium hexametaphosphate.
The fluid may have a viscosity of less than 100 centipoise when measured at 20xc2x0 C. and a shear rate of 200sxe2x88x921 using a Mettler Rheomat 180 Viscometer incorporating a double gap measuring geometry. Preferably, the viscosity is less than 50 centipoise, more preferably less than 30 centipoise when measured as aforesaid. Especially preferred is the case in which the viscosity is less than 20 centipoise.
The fluid may be applied to the support by any suitable means, which is preferably non-electrochemical.
The fluid may be applied to both sides of the support in order to form hydrophilic layers on both sides. A support with such a layer on both sides may be used to prepare a double-sided lithographic plate. Alternatively, if such a support is used for a single-sided plate, the side of the plate that does not carry an image layer may be protected by the hydrophilic layer. The fluid is preferably applied to only one surface of the support.
In the method, water is typically removed from the fluid after application. It is believed that, when a silicate liquid is used, this results in the silicate polymerizing, and thereby binding the particulate materials in position.
In a third aspect, the present invention is a printing member including non-ink accepting areas prepared according to the first aspect.
In a fourth aspect, the invention is any novel hydrophilizing means for rendering non-ink accepting a selected ink-accepting area of a printing member per se.
In a fifth aspect, the invention is the use of a hydrophilizing means as described herein for rendering non-ink accepting a selected ink-accepting area of a printing member.
In a sixth aspect, the invention is a method of printing using a printing member as described herein.
In a seventh aspect, the invention is a method of rendering non-ink accepting a selected ink-accepting area of a printing member, the method comprising contacting the selected area with a means (herein xe2x80x9cthe hydrophilizing meansxe2x80x9d) which renders the area non-ink accepting by covering the area.
The advantageous properties of this invention can be observed by reference to the following examples, which illustrate but do not limit the invention.